| 5998 | From the necessity of the past we can infer the impossibility of what never happens [Diod.Cronus, by White,MJ] |
| Full Idea: Diodorus' Master Argument inferred that since what is past (i.e. true in the past) is necessary, and the impossible cannot follow from the possible, that therefore if something neither is nor ever will be the case, then it is impossible. | |
| From: report of Diodorus Cronus (fragments/reports [c.300 BCE]) by Michael J. White - Diodorus Cronus | |
| A reaction: The argument is, apparently, no longer fully clear, but it seems to imply determinism, or at least a rejection of the idea that free will and determinism are compatible. (Epictetus 2.19) |
| 17183 | Things are impossible if they imply contradiction, or their production lacks an external cause [Spinoza] |
| Full Idea: A thing is said to be impossible either because the essence of the thing itself or its definition involves a contradiction, or because no external cause exists determinate to the production of such a thing. | |
| From: Baruch de Spinoza (The Ethics [1675], I Pr 33) | |
| A reaction: Is the contradiction in nature or in logic? How can he be sure that there doesn't exist some causeless thing? |
| 3946 | A thing is shown to be impossible if a contradiction is demonstrated within its definition [Berkeley] |
| Full Idea: A thing is shown to be impossible when a repugnancy is demonstrated between the ideas comprehended in its definition. | |
| From: George Berkeley (Three Dialogues of Hylas and Philonous [1713], II p.214) | |
| A reaction: The problem is always that imagination is needed to see the 'repugnancy', and that is relative and limited. |
| 9428 | Nothing we clearly imagine is absolutely impossible [Hume] |
| Full Idea: 'Tis an established maxim in metaphysics, that whatever the mind clearly conceives includes the idea of possible existence, or in other words, that nothing we imagine is absolutely impossible. | |
| From: David Hume (Treatise of Human Nature [1739], I.II.2) | |
| A reaction: It is important to note that this empiricist approach to what is impossible requires that we 'clearly' conceive the possibility - but how do we evaluate whether we are being clear or not? |
| 23283 | Necessity implies possibility, but in experience it matters which comes first [Williams,B] |
| Full Idea: Any notion of necessity must carry with it a corresponding notion of impossibility, …but it can make a difference which one of them presents itself first and more naturally. | |
| From: Bernard Williams (Practical Necessity [1982], p.127) | |
| A reaction: I like this because it connects modality with experience, rather than with formal logic. It seems right that in life we immediately see either a necessity or an impossibility, and inferring the other case is an afterthought. |
| 16426 | How can we know the metaphysical impossibilities; the a posteriori only concerns this world [Chalmers] |
| Full Idea: If some worlds are metaphysically impossible, it seems that we could never know it. By assumption the information is not available a priori, and a posteriori information only tells us about our world. | |
| From: David J.Chalmers (The Conscious Mind [1996], 2.4.2) | |
| A reaction: You need essentialism to reply to this. If you discover the essence of something, you can predict its possibilities. You discover the natures of the powers and dispositions of actuality. |
| 14377 | Possibilities are manifestations of some power, and impossibilies rest on no powers [Jacobs] |
| Full Idea: To be possible is just to be one of the many manifestations of some power, and to be impossible is to be a manifestation of no power. | |
| From: Jonathan D. Jacobs (A Powers Theory of Modality [2010], §4.2.1) | |
| A reaction: [This remark occurs in a discussion of theistic Aristotelianism] I like this. If we say that something is possible, the correct question is to ask what power could bring it about. |